Projecting warming's impact on Bay Area

TAKING THE HEAT

James Temple

Updated 1:02 am, Sunday, January 6, 2013

Mary Jane Schramm of the National Oceanic and Atmospheric Administration looks at the shore from the S.F. tide station.
Photo: Mike Kepka, The Chronicle

Mary Jane Schramm of the National Oceanic and Atmospheric...

Parts of a no longer operating tidal gauge lie at rest next to the oldest continuously operating tidal gauge in the Americas on Monday Nov. 27, 2012 in San Francisco, Calif.
Photo: Mike Kepka, The Chronicle

Parts of a no longer operating tidal gauge lie at rest next to the...

An obsolete tidal gauge, above and left, sits in the tidal observation station near Crissy Field, which has been in operation since 1854. Scientists say sea levels could surge nearly 6 feet by century's end because of climate change.
Photo: Mike Kepka, The Chronicle

It's now indisputable that the Earth is warming, at least for anyone who still takes thermometers at their word.

Average global temperatures have ticked up by about 0.8 degrees Celsius since 1880, and two-thirds of that increase has taken place since 1975, according to the National Aeronautics and Space Administration. Nine of the 10 warmest years in that time period have occurred since the year 2000.

To be sure, the planet has experienced cooling and warming periods in the past. But the steep temperature rise in the late 20th century blew past the highs of the last 1,000 years, the period for which there are reliable data.

And more warming is on the way. A variety of studies have concluded that current rates of fossil fuel emissions could push global temperatures up by as much as 6 degrees Celsius by 2100. To put that in context: A 2007 report by the U.N. Intergovernmental Panel on Climate Change predicts that an increase of just 3.5 degrees would drive into extinction 40 to 70 percent of the species for which the impact of global warming has been studied.

There is an overwhelming scientific consensus that fossil fuels are primarily to blame for the warming in recent decades. Nearly 98 percent of climate scientists actively publishing agree with that conclusion, according to a 2010 study by researchers at Stanford.

That study also found that the few researchers still unconvinced of what's known as anthropogenic climate change published far less on average in peer-reviewed climate literature, the accepted mark of scientific expertise and prominence.

Wildfires and floods

The consequences of a warming world are already making themselves known.

It's difficult to link any single season or weather event to climate change, but 2012 was a veritable case study in the patterns scientists have long warned could become the new normal. By midsummer, U.S. temperatures broke more than 40,000 daily heat records, and 2012 was almost certainly the warmest year on record. (The National Oceanic and Atmospheric Administration will report official December temperatures later this week.)

The resulting drought affected 80 percent of U.S. agricultural land, and the hot, dry conditions set the stage for one of the worst wildfire seasons in recent memory across the West.

In October, Superstorm Sandy, the largest Atlantic hurricane ever recorded, devastated the Eastern Seaboard, killing more than 100, knocking out power for millions and exacting an economic toll of more than $60 billion.

Munich Re, a global reinsurance company, released a study that same month underscoring a sharp increase in "weather-related loss events" over the past three decades. Nowhere was that more true than in the United States, where costly catastrophes like thunderstorms, tornadoes, wildfires, droughts and floods have nearly quintupled during that time.

Terra incognita

Without drastic changes to fossil fuel emissions, the impacts of global warming will land on the Bay Area with a brute force that pays no regard to our relatively liberal politics, farsighted state climate regulations or fondness for hybrid vehicles.

By 2050, rising sea levels could put land around the bay equivalent in area to six San Franciscos at risk of serious flooding, including the region's airports, a stretch of Silicon Valley high-tech campuses and the homes of more than 100,000 residents, according to the San Francisco Bay Conservation and Development Commission. Sea levels could surge nearly 6 feet by 2100, putting more than $60 billion in shoreline development in jeopardy.

The rising tides will also magnify the region's existing vulnerabilities to tsunamis and earthquakes, researchers say.

As California's temperatures climb, the Sierra snowpack that stores about a third of the state's water will dwindle. The increasing heat could also undermine the fog that feeds coastal ecosystems, including Northern California's treasured redwoods.

Land with the unique terroir necessary for the region's renowned grapes will shrink, devastating the wine and tourism sectors alike. Wild plant and animal species will migrate up hillsides and into different bodies of water, altering sensitive ecologies in complicated and unpredictable ways.

"It's terra incognita," said Jane Long, a former associate director at Lawrence Livermore National Laboratory and a visiting scientist at UC Berkeley. "We don't know where we're going, but we know we're heading toward something that could be very, very dangerous."